Tone color circuits for electrical organs



'May 28, 1963 w. MUNCH, .IR 3,091,148

TONE CCLCR CIRCUITS FCE ELECTRICAL CRCANS Filed Aug. 4, 1959 WALTER MUNCH, JR.

mwa/#M United States Patent O 3,091,148 TONE COLOR CIRCUITS EUR ELECTRiCAL ORGANS Walter Munch, Jr., Covington, Ky., assigner to The Baldwin Piano Company, Cincinnati, Chio, a corporation of Ohio Filed Aug. 4, 1959, Ser. No. 831,636 7 Claims. (Cl. SLi-1.19)

This invention relates to electrical organs, and is especially addressed to the obtaining of percussive effects in such instruments. As is well known, percussive effects simulating those of bells, bars, plucked strings and the like, may be obtained by sending the oscillations derived from a suitable generator through a gating circuit which causes the oscillations to die away gradually when the controlling playing key is released, and provided a tone color is imparted to the oscillations appropriate to the percussive tone generating device, e.g. a bell, which is being simulated. The percussive effect is primarily apparent when the instrument is played in a staccato fashion; and the percussive voices are thus adjunctive to the normal organ voices of the instrument.

While not so limited, the teachings of this invention may be thought of las applied to an electrical organ of the type described in U.S. Patent 2,233,948 to Kock, dated March 4, 1941. Such an instrument has a rank of electronic oscillators lor generators (which may be of the type shown in U.S. Patent 2,555,038 to Jones, dated May 29, 1951), the rank being divided into twelve groups of octavely related generators, the generator of highest frequency in each group acting as a master oscillator and controlling the submultiple frequencies of the other generators in the group. Oscillations from the generators are transmitted through gradual contact switches operated by the playing keys of the instrument t-o various headers or collectors, there being for each manual an 8 header, and a 4 or 116 header or both; and additional headers may be employed in more elaborate systems, with, of course, a multiplication of the switches operated by the keys.

In such instruments the generators produce complex oscillations rich in partials; and tone colors are obtained by sending the oscillations in the collectors, alone or in combination, through filter circuits which are controlled by stop switches. The lilter circuits are linear circuits of the formant type and do not generally involve electronic tubes or their equivalent. In some instances the oscillations in octavely related headers or collectors are combined in out-of-phase relationship to accentuate the odd order harmonics, and are then filtered to obtain woodwind effects. The oscillations, having passed through the selected filters are combined and transmitted to an amplifier and loud speaker constituting an output system.

The addition of percussion to a system of the type referred to involves the provision of an additional or new system between the generators and the output means. Oscillations from the several generators pass through gating circuits controlled by additional key switches (which in this instance may be simple make-and-break switches), there being a gating circuit for each generator within the range of percussion provided. The outputs of the gating circuits are not generally suitable for direct amplification and reproduction, nor are they generally suitable for modification of tone color by linear filters of the formant type. Consequently it has been the practice to send the oscillations through vacuum tube filter means before amplifying and reproducing them.

The copending application of Bissonette and Kramer, Serial No. 621,769, filed November 13, 1956 and en- 3,@9Ll48 Patented May 28, 1963 ICC titled Electronic Musical Instrument (assigned to the same assignee), now U.S. Patent 2,986,964 dated June 6, 1961, taught the use of vacuum tube amplification stages employing a negative feed back and a parallel T network, the network being tuned to exhibit a null at the fundamental frequency, the frequency response peaking sharply at the null frequency. Thus, if the null is at the fundamental frequency of the applied oscillations, the output of the vacuum tube filter will be substantially sinusoidal.

Bissonette and Kramer found that any one vacuum tube lter could handle the outputs of the gating circuits for as many as four adjacent semi-tones, which eifected some economy. Further, if a vacuum tube filter of the type referred to is energized by oscillations having a fundamental frequency which is a submultiple of the null frequency, a different voice could be obtained. Thus they were able to obtain several voices from a single rank of vacuum tube filters by a system of cross-connections rendered effective for different voices by several multicontact relays. But the cross-connections and relays involve a considerable complexity of wiring and substantial cost, so that the addition of percussion to the organ became a matter of substantial expense.

It is a primary object of this invention to provide a percussive system of very much less costly character, and greatly simplified, while having a satisfactory variety of tone colors.

It is an object of the invention to provide a percussive system which does not require the cross-connections above referred to.

It is an object of the invention to provide a percussive system which does not require multicontact relays, but in which the percussive voices may be selected by simple switches operated by the stop tabs of the instrument.

By the invention as hereinafter outlined it has become possible to provide percussion in relatively inexpensive electrical organs such as those now coming widely into use in the home.

These and other objects of the invention which will be pointed out hereinafter or will be apparent to one skilled in the art upon reading these specifications are accomplished by that arrangement of parts of which an exemplary embodiment will now be described. Reference is made to the accompanying drawings wherein:

FIG. -l is a diagrammatic representation of the type of vacuum tube filter employed in the invention.

FIG. 2 is a partial diagrammatic representation of the percussive system of this invention.

In the drawings, the oscillators or generators have not been shown, nor has an output system, since, as hereinabove indicated, these may be the corresponding elements in the Kock patent.

In the practice of this invention, oscillations are derived from the generators through the gating circuits which are controlled by simple make-andbreak switches operated yby the playing keys in addition to the gradual contact switches used in the normal organ sections. The derived oscillations pass through separate leads to separate gating circuits having the function already outlined. Various kinds of gating circuits may lbe used. A :common kind is a vacuum tube amplifier stage in which the tube is biased to eut-ofi, the closing :of the key switch acting to eliminate the cut-off bias. An RC time delay circuit acts, when the switch is opened upon release of the key to restore the bias in a gradual manner, so that Ithe tone dies away at a predetermined rate. `One such circuit is taught in the Bissonnette and Kramer application Serial No. 621,769 above referred to. An improved circuit of this type, making it `easier to secure different rates of decay selectively for different effects is shown in the copending application of `the present inventor, Serial No. 621,807 filed November 13, 1956 and entitled, Percussive Circuit and Assembly, now Patent 2,918,576, issued December 22, 1959. This also may 'be used as well as the selective rate control means taught in connection therewith. The neon tube gating circuits disclosed in the copending application of the present inventor, Serial No. 657,085, filed May 6, 1957 and entitled, Keying System for Electrical Musical Instruments may be employed, as well as many others. These have not been illustrated in det-ail.

The vacuum tube filter used in the present invention is a modified bridged T amplifier illustrated in FTG. 1 hereof. The thermionic triode 1.3 has its grid connected through a resistor 114 and a capacitor 15 to a gating circuit (or combination of gating circuits as hereinafter explained). The plate of the tube is connected to a suitable source of B| voltage through a resistor 16. The cathode is connected to ground or the common return through a resistor 17. There is a feed back connection between the plate and grid containing a capacitor 18 and a bridged T network, comprising resistors 19 and 2d in T formation with a capacitor 21 therebetween and normally connected to ground. The resistors are bridged Aby a capacitor 22.

Instead of lconnecting capacitor 21 directly to ground, however, it is connected to a header 23 to which the bridged T ground leads of all of the other vacuum tube filters in the rank are also connected. This makes it possible to break the ground connection for all vacuum .tu-be filters simultaneously, serving a purpose hereinafter to be described.

Two output leads are shown. One, containing a resistor 24 goes to a header 25 called, for convenience a ute header. Another, containing a resistor 26 goes to a header 27 called, for convenience a string header.

The bridged T amplifier acts as a fairly broadly tuned band pass filter. This makes it possible for any one vacuum tube filter to handle the outputs of as many as six gating circuits for oscillations related successively as adjacent semitones. Thus the number of vacuum tube filters required is greatly cut down. More importantly, the output of the vacuum tube filter is rich enough in harmonics to be susceptible (along -with the outputs of the other vacuum filters in the rank) yto tone color modihcation by linear `or formant lter means. Thus, the use of various low pass lfilters will give a variety of flute tones. High pass filters impart a string-like tonality. Yet again, it has been found that if the ground connection of the bridged T network is opened, part of the filtering action will be destroyed, thus providing more harmonies. String-likevoices are preferably obtained by breaking the ground connection and applying high pass filtering to the combined outputs of the vacuum tube filters.

Where each vacuum tube filter is connected to a group of gating circuits, the bridged T network of the filter is tuned to the fundamental of the oscillations transmitted by the median gating circuit-in the group.

The simplicity of the systemV of this invention is illustrated in FIG. 2. The index numerals 1 to 12 and 31 to 36 have been used to indicate the first two and last groups of six leads each from generators to their respective gating circuits in an instrument in which percussion is provided over a range of 36 semitones. There will be a gating circuit for each of the 36 oscillators; but the gating circuits are divided into groups of six, havin-g combined outputs. Three 4of the groups are indicated at 28, 29 and 3ft.

AOne bridged T vacuum tube filter receives the output of each group of 4gating circuits; and three of` the filters have been diagrammatically indicated at 37, 38 and 39. As has been explained, these vacuum tube filters have a common ground header 23, a common fiute header 25, and a common string header 27. The flute header is shown as connectible to an output header or collector dit through a low pass filter 41 and a stop switch 42. The low pass filter need not be described in detail. `On the drawing it is designated as producing a Vibra-Harp voice, and in this connection it may fbe noted that the vibrato characteristic of such voice will be derived from the original generators in the system of the Kock patent. Other low pass filters may be interposed between the flute header 25 and the output header 40 to provide other voices of generally flute-like quality.

A high pass -filter 43 and a stop switch idhas been shown interposed between the string header 27 and the output header 40. In the drawing this has been designated as producing an Organ-Harp voice. Here again other voices may be obtained by the use of other high pass linear filters.

The common ground lead 23 of the several vacuum tube filters is connected to ground at 45 through a switch 46. The string header 27 is connected to the output header lll `through a high pass filter 47 and a stop switch 48 for the production of a String-Percussion voice. The switches 46 and 48k are coupled so that when the stop switch 48 closes the ground switch 46 will operi .to provide the effect described above. Other string percussion voices may be obtained in the' same fashion through the' use of other high pass filters.

The output header has an output lead 49 which will be tuiderstood as connected to the output system of the instrument.

Modifications may be made in the invention without departing from the spirit of it. The invention having been described in an exemplary embodiment, what is claimed as new and desired to b'e secured by Letters Patent is:

`1. In an electrical organ having generators for producing complex oscillations and anV output system, a percussive system comprising gating circuits coupled to said generators and actuable by playing key switches, bridged T amplifier circuits receiving the outputs of said gating circuits, a first header receiving the outputs of said bridged T amplifiers, an output header, and a linear filter means interposed between' said first header and said output header.

2.. The structure claimed in claim 1 wherein a second header is also arranged to receive the outputs of said bridged T amplifiers, wherein a linear filter means is interposed between said second header and said output header, and wherein said first mentioned linear filter means is a low pass filter and said second mentioned linear filter means is a high pass filter.

3. The structure claimed in claim l wherein saidv bridged T amplifiers have ground connections, wherein said connections are rnade to a ground header, and wherein a switch is interposed between said ground header and ground whereby the ground connections of all of said bridged T amplifiers may be broken simultaneously.

4. The structure claimed in claim 2 wherein said bridged T amplifiers have ground connections, wherein said connections are made to a ground header, and wherein a switch is interposed ybetween said ground header and ground whereby the ground connections of all of said bridged T amplifiers may be broken simultaneously, wherein there is a low pass filter and a stop switch interposed between said second header -and'said output header, and wherein said ground switch and said stop switch are coupled in such a way that when saidstop switch is closed said `ground switch is opened.

5. The structure claimed in claim 4 wherein said gating circuits are divided into groups of sixV gating circuits `for adjacent semitones and wherein there is yal bridged T amplifier for each such group.

6. 1in an electrical organ having generators and a keying system for selecting oscillations in accordance with the requirements of a musical composition, and an output system, `a bridged T amplifier receiving oscillations from at least one generator, and a linear filter means interposed between said amplifier and the output system.

breaking its connection to ground.

References Cited in the le of this patent UNITED STATES PATENTS Kock Mar. 4, 1941 'Jordan May 29, 1951 6 yMork June 19, 1951 Marchand Sept. 14, 1954 Faulkner Oct. 29, 1957 Oncley July 8, 1958 Zomber Feb. 9, 1960 FOREIGN PATENTS France July 9, 1959 

1. IN AN ELECTRICAL ORGAN HAVING GENERATORS FOR PRODUCING COMPLEX OSCILLATIONS AND AN OUTPUT SYSTEM, A PERCUSSIVE SYSTEM COMPRISING GATING CIRCUITS COUPLED TO SAID GENERATORS AND ACTUABLE BY PLAYING KEY SWITCHES, BRIDGED T AMPLIFIER CIRCUITS RECEIVING THE OUTPUTS OF SAID CIRCUITS, A FIRST HEADER RECEIVING THE OUTPUTS OF SAID BRIDGED T AMPLIFIERS, AN OUTPUT HEADER, AND A LINEAR FILTER MEANS INTERPOSED BETWEEN SAID FIRST HEADER AND SAID OUTPUT HEADER. 